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Moisture inflow over the Po Valley and orographic precipitations during MAP IOP 8: analysis using GPS network, satellite observations and weather prediction model simulations
PAPER WITHDRAWN
Olivier M. Bock, IPSL/CNRS, Paris, France; and C. N. Flamant, E. Richard, J. Tournadre, and J. R. Pelon
An analysis of integrated water vapor (IWV) obtained from Global Positioning System (GPS) measurements has been carried out over the Alps throughout October 1999. IWV was derived from zenith path delay parameters estimated every two hours during the GPS data analysis. The accuracy of the retrieval has been assessed through a comparison with balloon sounding data for different GPS data analysis strategies. The bias and RMS errors of GPS-derived IWV is estimated to 0.5 kg/m2 and 1.4 kg/m2, respectively. Further comparisons are presented between GPS and satellite observations (SSM/I) and analyses from the ECMWF model. These data have been used to investigate more precisely the evolution of the water vapor content during MAP IOP 8. Especially we tried to evaluate the role of the moisture inflow from the Mediterranean over northern Italy in the persistence of precipitation in the Lago Maggiore region. To investigate this, two-dimensional maps of IWV have been derived by interpolating GPS retrievals from a network of GPS stations over Italy and Europe. They showed a strong increase of water vapor content in the Po Valley, peaking at 21 October 99, 1200 UTC at Milano. This was consistent with the sharp increase of water vapor content over the Adriatic Sea observed by SSM/I and the easterly surface wind observed by QuickScat and ECMWF analyses. The high temporal resolution of GPS retrievals were very valuable for monitoring the evolution of the water vapor content over land where satellite observations are lacking. In order to separate of the contribution of the lower 4 km of the troposphere from the total water content, GPS stations at different altitudes are used. This allows to estimate the water vapor inflow from the Adriatic Sea feeding the convective system precipitating in the Lago Maggiore region. This separation between lower and upper tropospheric water vapor content is also compared to IWV contents determined from ECMWF analyses.
Session 7, Orographic Precipitation II
Tuesday, 18 June 2002, 10:15 AM-1:29 PM
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